[Form] Example of customizing EnumType labels

Default behavior when creating a EnumType form element is that the choice labels displayed to the user are the enum names. 

This PR adds an example of how to use a function inside an enum to return labels and how to bind this function to the form element.

Author: robinbrisa

reference/forms/types/enum.rst

@@ -52,6 +52,40 @@ This will display a ``<select>`` tag with the three possible values defined in
 the ``TextAlign`` enum. Use the `expanded`_ and `multiple`_ options to display
 these values as ``<input type="checkbox">`` or ``<input type="radio">``.
 
+Since the label displayed in the ``<select>`` options is the enum name, you might sometimes
+want more flexibility as PHP strongly restricts the usable characters for those.
+You could do this by implementing a function in your enum class which returns a label 
+or even a translation string for each possible enum::
+
+    // src/Config/TextAlign.php
+    namespace App\Config;
+
+    enum TextAlign: string
+    {
+        case Left = 'Left/Start aligned';
+        case Center = 'Center/Middle aligned';
+        case Right = 'Right/End aligned';
+        
+        public function label(): string
+        {
+            return match ($this) {
+                self::Left => 'text_align.left.label',
+                self::Center => 'text_align.center.label',
+                self::Right  => 'text_align.right.label',
+            };
+        }
+    }
+    
+You can then use the ``choice_label`` option of ``EnumType`` with a function that 
+returns the label::
+
+    ->add('textAlign', EnumType::class, [
+        'class' => TextAlign::class,
+        'choice_label' => static function (TextAlign $choice): string {
+            return $choice->label();
+        },
+    ])
+
 Field Options
 -------------